Lighting system including a power backup device

ABSTRACT

A system may include a light source. A converter may be configured to convert an AC voltage to a DC operating voltage during normal operation. A power backup device may be coupled to the converter. A current source may have a first terminal configured to receive the DC operating voltage during regular operation and a second terminal configured to provide a pulse-width modulated (PWM) signal to an anode end of the light source. A switching device may have a first connecting terminal coupled to the anode end of the light source, a second connecting terminal coupled to the power backup device, and a control terminal coupled to the converter. The switching device may be configured to open a switch between the first connecting terminal and the second connecting terminal during normal operation and close the switch upon detecting an interruption of the DC operating voltage at the control terminal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/730,386, filed Oct. 12, 2017, which claims the benefit of U.S.Provisional Application No. 62/407,382, filed Oct. 12, 2016, U.S.Provisional Application No. 62/426,085, filed Nov. 23, 2016, and EPPatent Application No. 17155961.0, filed Feb. 14, 2017, which areincorporated by reference as if fully set forth.

BACKGROUND

Safety codes in many municipal jurisdictions often require the provisionof sufficient and suitable lighting in buildings to ensure thereasonable safety of persons entering and exiting the buildings. Thisincludes a requirement to provide emergency lighting to enable personsto escape from buildings when mains power is not available.

Emergency lighting systems commonly include a power backup device thatis designated to provide backup power in the event of a mains poweroutage. Light fixtures in those systems are often wired to the powerbackup device and the power grid at the same in time. However, because asingle power backup device can be used to power multiple light fixtures,some lighting systems include lengthy wire runs between their lightfixtures and their power backup device. Having lengthy wire runs can beproblematic in instances in which pulse-width modulated (PWM) signalsare used to drive the light fixtures. In such instances, the wires canbecome a source of parasitic inductance, which can cause voltage spikesand ringing. Accordingly, the need exists for improved lighting systemdesigns that avoid the generation of large amounts of parasiticinductance.

SUMMARY

A system may include a light source. A converter may be configured toconvert an AC voltage to a DC operating voltage during normal operation.A power backup device may be coupled to the converter. A current sourcemay have a first terminal configured to receive the DC operating voltageduring regular operation and a second terminal configured to provide apulse-width modulated (PWM) signal to an anode end of the light source.A switching device may have a first connecting terminal coupled to theanode end of the light source, a second connecting terminal coupled tothe power backup device, and a control terminal coupled to theconverter. The switching device may be configured to open a switchbetween the first connecting terminal and the second connecting terminalduring normal operation and close the switch upon detecting aninterruption of the DC operating voltage at the control terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described below are for illustration purposes only. Thedrawings are not intended to limit the scope of the present disclosure.Like reference characters shown in the figures designate the same partsin the various embodiments.

FIG. 1 is a circuit diagram of a lighting system, according to the priorart;

FIG. 2 is a circuit diagram of a lighting system, according to aspectsof the disclosure;

FIG. 3 is a state diagram illustrating the operation of the lightingsystem of FIG. 2, according to aspects of the disclosure;

FIG. 4 is a flowchart of an example of a process performed by thelighting system of FIG. 2 when the lighting system of FIG. 2 is in afirst state, according to aspects of the disclosure; and

FIG. 5 is a flowchart of an example of a process performed by thelighting system of FIG. 2 when the lighting system of FIG. 2 is in asecond state, according to aspects of the disclosure.

DETAILED DESCRIPTION

According to aspects of the disclosure, an improved lighting system isdisclosed that generates reduced amounts of electromagnetic interference(EMI). The lighting system may include one or more light-emitting diodes(LEDs) which are powered using a pulse-width modulated (PWM) signal. ThePWM signal has the potential to create large amounts of EMI whentransmitted over long runs of cable. The improved lighting system,however, features a topology that reduces the amount of EMI that isgenerated by the transmission of PWM signals. In this topology, PWMsignals are delivered to the LEDs via comparatively short runs of cableto reduce the amount of EMI produced by the lighting system.

Examples of implementations of the improved lighting system will bedescribed more fully hereinafter with reference to the accompanyingdrawings. These examples are not mutually exclusive, and features foundin one example can be combined with features found in one or more otherexamples to achieve additional implementations. Accordingly, it will beunderstood that the examples shown in the accompanying drawings areprovided for illustrative purposes only, and they are not intended tolimit the disclosure in any way. Like numbers refer to like elementsthroughout.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element such as a layer, region orsubstrate is referred to as being “on” or extending “onto” anotherelement, it can be directly on or extend directly onto the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on” or extending “directlyonto” another element, there are no intervening elements present. Itwill also be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. It will be understood that these terms areintended to encompass different orientations of the element in additionto any orientation depicted in the figures.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “vertical” may be used herein to describe a relationshipof one element, layer or region to another element, layer or region asillustrated in the figures. It will be understood that these terms areintended to encompass different orientations of the device in additionto the orientation depicted in the figures.

FIG. 1 is a circuit diagram of a lighting system 100, in accordance withthe prior art. The lighting system 100 includes a power backup device112 and an AC-to-DC converter 116 which are both connected to an ACpower supply. The AC power supply may include a municipal power grid,and/or any other suitable source of line voltage. The AC-to-DC converter116 is configured to power both a light source 120 and a light source124 when power from the AC power supply is available. The power backupdevice 112, on the other hand, is configured to power only the lightsource 124 when the supply of power to the AC-to-DC converter 116 isinterrupted in the event of a failure of the AC power supply (e.g., amains power outage, etc.).

The power backup device 112 may include a battery 114, a switch K1, anda switch K2. When power from the AC power supply is available, theswitch K1 is configured to connect line 144 to line 146 in order toroute power from the current source 122 to the light source 124.Furthermore, when power from the AC power supply is available, theswitch K2 is configured to disconnect the negative terminal of thebattery 144 from the return path of the light source 124. When thesupply of power from the AC power supply is interrupted, the switch K1is re-configured to disconnect the wire 144 from the wire 146.Furthermore, when the supply of power from the AC power supply isinterrupted, the switch K2 is re-configured to connect the negativeterminal of the battery 114 to the return path of the light source 124.Connecting the negative terminal of the battery to the light source 124ensures that the light source 124 can remain operational while powerfrom the AC power supply is unavailable. Stated succinctly, according tothe arrangement shown in FIG. 1, the positive terminal of the battery114 is connected to the current source 124 at all times, while thenegative terminal of the battery 114 is connected to the return path ofthe light source 124 only when power from the AC power supply is notavailable.

The light source 120 may include one or more LEDs. Similarly, the lightsource 124 may also include one or more LEDs. The LEDs in the lightsource 120 may be configured to emit light having a first colortemperature, and the LEDs in the light source 124 may be configured toemit light having a second color temperature that is different from thefirst color temperature. For example, the LEDs in the light source 120may be configured to emit light having a color temperature of 3000K, andthe LEDs in the light source 124 may be configured to emit light havinga color temperature of 4000K.

The light source 120 may be driven by a current source 118 and the lightsource 124 may be driven by a current source 122. The current source 118may be configured to generate a PWM signal based on a control signalCTRL received from a controller 140. The duty cycle of the PWM signalmay depend on the control signal CTRL that is provided by the controller140, and it may determine the brightness of the LEDs in the light source120. The current source 122 may similarly be configured to generate aPWM signal based on the control signal CTRL. The duty cycle of the PWMsignal generated by the current source 122 may also depend on thecontrol signal CTRL that is provided by the controller 140, and it maydetermine the brightness of the LEDs in the light source 124. Statedsuccinctly, the controller 140 may use the control signal CTRL to adjustthe brightness level of the light sources 120 and 124.

The controller 140 may include a processor (not shown) and a Bluetoothinterface (not shown). The processor may be configured to generate thecontrol signal CTRL (alone or in combination with other circuitry) basedon a voltage signal DIM that is generated by the dimmer interface 132.The dimmer interface 132 may be configured to generate the referencevoltage signal based on an input signal that is fed to the dimmerinterface 132 by the dimmer controller 126. The dimmer controller 126may include a slider switch or a knob, which can be physicallymanipulated by a user in order to set the brightness of the lightsources 120 and 124.

The controller 140 and the dimmer interface 132 may be powered by theDC-to-DC converter 130. The DC-to-DC converter 130 may include a voltageregulator (not shown) that is operable to lower the 48V DC signalprovided by the AC-to-DC converter 116 to 12V and subsequently feed the12V signal to the dimmer interface. Furthermore, the DC-to-DC convertermay include a linear regulator (not shown) that is operable to furtherreduce the 12V DC signal provided by the voltage regulator to 3.3V DCand subsequently feed the 3.3V signal to the controller 140.

The PWM signal that is used to power the light source 124 is routedthrough the power backup device 112 via the lines 144 and 146. Thispermits the power backup device 112 to control whether the battery 114or the AC-to-DC converter 116 supplies the power to the LEDs, which inturn eliminates the possibility of double-driving the light source 124when there is a power fluctuation. It further permits the execution oftesting sequences for testing the operational readiness of the lightingsystem 100 in the event of a power outage.

According to the design of the lighting system 100, the PWM signaloutput from the current source 122 is routed through the lines 144 and146 before it reaches the light source 124. The lines 144 and 146 (e.g.,wires, cables, power rails, etc.) can be over a meter long and they canreach up to 15 meters each in some products that are available on themarket. Having lines this long may be necessitated, for example, by thepower backup device 112 being located far away from the light source 124or a need for the power backup device 112 to power multiple lightfixtures that are some distance apart from one another.

During normal operation, when power from the AC power supply isavailable, the PWM signal (e.g., a 1 kHz PWM signal) generated by thecurrent source 122 for the light source 124 is routed through the powerbackup device 112 via the switch K1 which connects the lines 144 and 146to one another. The long wires 144/146 conducting the PWM signal(current) through the power backup device 112 may introduce parasiticinductances. As can be readily appreciated, currents at the PWMfrequency, having rise and fall times on the order of 1 microsecond, cancause significant EMI. The corner frequency of the resulting EMI signalmay be on the order of 300 kHz. In some aspects, the use of largecapacitors C0 and C1 somewhat reduces the EMI, but also reduces thesharpness of the PWM pulses, which affects the accuracy of thebrightness and color control. Further, even if the capacitors C0 and C1were not used, the parasitic capacitances and inductances on the lines144 and 146, which as noted above could be up to 15 m long, could alsocause inconsistent performance due to PWM currents flowing through them.

FIG. 2 is a circuit diagram of a lighting system 200, according toaspects of the disclosure. The lighting system 200 includes a powerbackup device 212 and an AC-to-DC converter 216 which are both connectedto an AC power supply 260. The AC power supply 260 may include amunicipal power grid, and/or any other suitable source of line voltage.The AC-to-DC converter 216 may be configured to power both a lightsource 220 and a light source 224 when power from the AC power supply260 is available. The power backup device 212, on the other hand, may beconfigured to power only the light source 224 when the AC-to-DCconverter 216 is switched off as a result of the supply of power fromthe AC power supply 260 being interrupted.

The power backup device 212 may include a battery 214, and switches S1and S2. Each of switches S1 and S2 may include a spring-loaded relayswitch and/or any other suitable type of switching device. In someimplementations, the power backup device 212 may further includecurrent-sensing circuitry (not shown) that is arranged to detect whenthe supply of power from the AC power supply 260 is interrupted. In someimplementations, the current-sensing circuitry of the power backupdevice 212 may be configured to open the switch S1 and close the switchS2 in response to detecting that the supply of power from the AC powersupply 260 is interrupted. The current-sensing circuitry of the powerbackup device 112 may also detect when the supply of power from the ACpower supply 260 is resumed and, in response, open the switch S2 whileconcurrently closing the switch S1. Accordingly, in someimplementations, the current sensing circuitry may at least in parttransition the power backup device 212 between two different states byreconfiguring the switches S1 and S2 based on whether power from the ACpower supply 260 is available.

More specifically, when a supply of power from the AC power supply 260is available, switch S1 may be configured by the current-sensingcircuitry of the power backup device 212 to connect line 244 to line246, thus causing the positive terminal of the AC-to-DC converter 216 tobe connected to the input terminal T1 of the current source 222. At thesame time, the switch S2 may be configured by the current-sensingcircuitry of the power backup device 212 to maintain an open circuitbetween the negative terminal of the battery 214 and the return path 248of the light source 224. In some implementations, the lines 244 and 246(e.g., wires, cables, power rails, etc.) may be substantially longerthan the lines spanning from the output terminals To of the currentsources 118 and 222 to the anodes of the light sources 220 and 224.Specifically, in some implementations, the lines 244 and 246 may bebetween 1 m and 15 m long. As is further discussed below, in system 200,no PWM signals are carried over the lines 244 and 246 which reduces theamount of EMI that is produced by the system 200 (in comparison to thesystem 100).

Furthermore, when a supply of power from the AC power supply 260 isinterrupted, switch S1 may be configured by the current-sensingcircuitry of the power backup device 212 to disconnect line 244 fromline 246, thus causing the positive terminal of the AC-to-DC converterto be disconnected to the input terminal T₁ of the current source 222.At the same time, the switch S2 may be configured by the current-sensingcircuitry of the power backup device 212 to close the circuit betweenthe negative terminal of the battery 214 and the return path 248 of thelight source 224.

As illustrated in FIG. 2, the positive terminal of the battery 214 maybe connected at all times to the input terminal T₁ of the current source222. Furthermore, the negative terminal of the battery 214 may beconnected to the return path 248 of the light source 224 only when thesupply of power from the AC power supply 260 is interrupted. However,alternative implementations are possible in which the negative terminalof the battery is always connected to the return path 248 while anotherswitching device, is used to connect line 246 to one of line 244 and thepositive terminal of the battery 214.

The light source 220 may include one or more LEDs. The LEDs in the lightsource 220 may be disposed in the same light fixture or in a pluralityof light fixtures that are some distance apart from one another.Similarly, the light source 224 may also include one or more LEDs. TheLEDs in the light source 224 may also be disposed in the same a lightfixture or in a plurality of light fixtures that are some distance apartfrom one another. According to aspects of the disclosure, the LEDs inthe light source 220 may be configured to emit light having a firstcolor temperature, and the LEDs in the light source 224 may beconfigured to emit light having a second color temperature that isdifferent from the first color temperature. For example, the LEDs in thelight source 220 may be configured to emit light having colortemperature of 3000K and the LEDs in the light source 224 may beconfigured to emit light having a color temperature of 4000K.

The light source 220 may be driven by a current source 218 and the lightsource 224 may be driven by a current source 222. The current source 218may be configured to generate a PWM signal for driving the light source220 based on a control signal CTRL received from a controller 240. Theduty cycle of the PWM signal may depend on the control signal CTRL, andit may determine the brightness of the LEDs in the light source 220. Thecurrent source 222 may be similarly configured to generate a PWM signalfor driving the light source 224 based on the control signal CTRL. Theduty cycle of the PWM signal generated by the current source 222 mayalso depend on the control signal CTRL that is provided by thecontroller 240 and determine the brightness of the one or more LEDs inthe light source 224. Stated succinctly, the control signal CTRLprovided by the controller 240 may set the brightness level of the lightsources 220 and 224.

The switching device S3 and the current source 222 may be coupled inparallel to the light source 224 and the power backup device 212. Thecurrent source 222 may be arranged on a first electrical path betweenthe power backup device 212 and the light source 224 and the switchingdevice S3 may be arranged on a second electrical path between the powerbackup device 212 and the light source 224. The first electrical pathmay span nodes N1, N2, and N3. And the second electrical path may spannodes N1, N4, N5, N2, and N3. In some implementations, the differencebetween the first electrical path and the second electrical path may bein that the first electrical path does not extend: (1) between nodes N1and N4 and (2) between nodes N4 and N5, while the second electrical pathdoes not extend (3) between nodes N1 and N2.

The switching device S3 may include a control terminal C_(T) and twoconnect-terminals T. The switching device S3 may be configured toselectively connect and disconnect the connect-terminals T from oneanother based on the value of a signal that is applied at the controlterminal C_(T). When a first signal is applied at the control terminalC_(T) (e.g., 48V), the switching device S3 may open an electrical pathbetween the connect-terminals T. In such instances, no current may flowbetween the connect-terminals (across the switching device S3) and theswitching device S3 is said to be in an open state. When a second signalis applied at the control terminal CT (e.g., 0V), the switching deviceS3 may close the electrical path between the connect terminals T. Insuch instances, current may flow across the switching device S3, betweenthe connect-terminals T, and the switching device S3 is said to be in aclosed state.

In the present example, one of the connect-terminals is coupled to thebattery 214 and the other-connect terminal is coupled to the anode endof the light source 224. When a first signal is applied on the controlterminal C_(T) (e.g., 48V), the switching device S3 may maintain anelectrical path between the two connect-terminals T open. When a secondsignal is applied on the control terminal C_(T) (e.g., 0V), theswitching device S3 may close the electrical path between the twoconnect-terminals T. In some implementations, a diode 288 may beprovided at the output terminal T_(O) of the current source 222 toprevent the backflow of current. The capacitors C2 and C2 may be coupledto the lines 246 and 250 to filter out some types of noise, such asswitching noise generated by the switching device S3.

The switching device S3 may include any suitable type of switchingdevice. In some implementations, the switching device S3 may include aPMOS transistor. In such instances, the control terminal C_(T) of theswitching device S3 may be the gate of the PMOS transistor. Furthermore,in instances in which the switching device S3 includes a PMOStransistor, the gate of the PMOS transistor may be coupled to a simpleVgs limiting circuit, such as a Zener diode, to limit the voltage at thegate. The Vgs limit may be on the order of 20V.

The controller 240 may include a processor (not shown) and acommunications interface (not shown), such as a Bluetooth interface. Theprocessor may include one or more of a general-purpose processor, anapplication-specific integrated circuit (ASIC), a Field-ProgrammableGate Array (FPGA), and or any other suitable type of processingcircuitry. The processor may be configured to generate the controlsignal CTRL (alone or in combination with other circuitry) based on areference voltage signal DIM that is generated by the dimmer interface232. The dimmer interface 232 may be configured to generate thereference voltage signal based on an input signal that is fed to thedimmer interface 232 by the dimmer controller 226. In someimplementations, the dimmer controller 226 may include a slider, aswitch, a knob, and/or another similar device that can be physicallymanipulated by a user to change the brightness of the light sources 220and 224. The controller 240 may be powered by a DC-to-DC converter 230,which may be operable to further reduce the 48V DC signal output by theAC-to-DC converter to 3.3V DC.

When power from the AC power supply 260 is available, the switch S1 maybe maintained in a closed state by the current-sensing circuity of thepower backup device 212, and the switch S2 may be maintained in an openstate by the current-sensing circuitry of the power backup device 212.Concurrently, a 48V DC signal (e.g., DC operational voltage) may begenerated by the AC-to-DC converter 216 and routed through the switch S1of the power backup device 212 and into the current source 222. A PWMsignal may be generated by the current source 222 based on the 48V DCsignal (e.g., DC operational voltage) and used to power the light source224. Because no PWM signal is carried over the lines 244 and 246 thatconnect the current source 222 to the power backup device 212, theamount of EMI generated by the lighting system 200 is greatly reduced.This is partly due to the fact that the lines 244 and 246 may be muchlonger than the lines connecting the output terminals of the currentsources to the light sources. Furthermore, this is in contrast to thelighting system 100, in which the wires that connect the current source122 to the power backup device 112 carry PWM signals, which in turncauses increased amounts of EMI. It will be recalled that connecting thecurrent source(s) 122/222 to the respective power backup devices 112/126may be necessary for various practical reasons, such as ensuring that noLEDs are double-driven and/or performing testing sequences.

Furthermore, when current from the AC power supply 260 is available, a48V DC signal (e.g., DC operational voltage) may be applied at thecontrol terminal C_(T) of the switching device S3 by the AC-to-DCconverter 216, which may cause the switching device S3 to remain in theopen state.

When the supply of power from the AC power supply 260 is interrupted,the controller 240 may be switched off as a result of having its powersupply cut off. When the controller 240 is switched off, it may nolonger supply the control signal CTRL to the current source 222, whichin turn may cause the current source 222 to become disabled. When thecurrent source 222 is disabled, the electrical path between the inputterminal T_(I) and the output terminal T_(O) of the current source 222is interrupted and no current can flow across the current source 222from the power backup device 212 to the light source 224.

Furthermore, when the supply of current from the AC power supply 260 isinterrupted, the current-detecting circuit (not shown) of the powerbackup device 212 may detect the interruption. In response, thecurrent-detecting circuit (not shown) of the power backup device 212 mayreconfigure (e.g., open) switch S1 to disconnect line 244 from line 246,thus leaving line 246 connected only to the positive terminal of thebattery 214. Furthermore, in response to detecting that the supply ofpower from the AC power supply 260 has been interrupted, thecurrent-detecting circuit of the power backup device 212 may reconfigure(e.g., close) the switch S2 to connect the return path of the lightsource 224 to the negative terminal of the battery 214. Concurrently,when the supply of power from the AC power supply 260 has beeninterrupted, the signal applied at the control terminal C_(T) of theswitching device S3 by the AC-to-DC converter 216 may change to a logiclow value (e.g., 0V), which in turn may cause the switching device S3 totransition into the closed state, thus connecting the positive terminalof the battery 214 to the light source 224. As a result of thereconfiguration of the switches S1, S2, and S3, the light source 224 maybegin receiving power from the power backup device S3 and remainoperational in the event of a failure of the AC power supply 260 (e.g.,in the event of a mains power outage).

FIG. 3 is a state diagram illustrating the operation of the lightingsystem 200, according to aspects of the disclosure. FIG. 3 shows thatduring its operation, the system 200 may cycle between at least twooperational states, termed “normal power state” and “backup powerstate.”

When the system 200 is in the normal power state, the light sources 220and 224 are both powered by the AC-to-DC converter 216. Moreparticularly, when the system 200 is in the normal power state, a supplyof AC voltage from the AC power supply 260 is available to the AC-to-DCconverter 216, which converts the AC voltage to a 48V DC operationalvoltage. As discussed above, the 48V DC operational voltage may be usedto drive various components of the system 200, such as the controller240, and the current sources 218 and 222. When the system 200 is in thenormal power state, the lines 244 and 246 may be connected to oneanother by the switch S1, while the negative terminal of the battery 214may be disconnected from the light source 224 by the switch S2.Furthermore, the switching device S3 may be in the open state as aresult of having the operational DC voltage applied by the AC-to-DCconverter 216 at the switching device's S3 control terminal C_(T).

When the system 200 is in the backup power state, the light source 220is switched off, while the light source 224 is powered by the powerbackup device 212. More particularly, when the system 200 is in thebackup power state, the supply of AC voltage from the AC power supply260 is interrupted. As a result, the AC-to-DC converter 216 may stopoutputting the 48V DC operational voltage, causing the controller 240 tobecome switched off. When the controller 240 is switched off, thecontrol signal CTRL stops being supplied to the current source 222 bythe controller 240. When the control signal CTRL is not supplied to thecurrent source 222, the electrical path between the input and outputterminals of the current source 222 is interrupted such that no currentfrom the power backup device 212 can flow across the current source 222.Furthermore, line 244 is disconnected from line 246 by the switch S1,while the negative terminal of the battery 214 is connected to thereturn path 248 of the light source 224 by the switch S2. Furthermore,in the backup power state, the switching device S3 is transitioned intothe closed state (as a result of a the 48V DC operational voltage nolonger being applied at the control terminal C_(T) by the AC-to-DCconverter 216), which permits current from the battery 214 to flowacross the switching device S3 and into the light source 224.

The system 200 may exit the normal power state and transition into thebackup power state when the current sensing circuit in the power backupdevice 212 detects that the supply of power from the AC power supply 260has been interrupted, causing the AC-to-DC converter 216 to lose itssupply of AC voltage and stop receiving any power. The system 200 mayexit the backup power state and transition into the normal power state,when the current sensing circuit in the power backup device 212 detectsthat the supply of power from the AC power supply 260 has been resumed,causing the supply of AC voltage to the AC-to-DC converter 216 to beavailable.

FIG. 4 is a flowchart of an example of a process 400 that is performedby the system 200 when the system 200 is in the normal power state. Atstep 410, switch S1 is configured to connect lines 244 and 246 to oneanother, and the switch S2 is configured to disconnect the negativeterminal of the battery 214 from the return path 248 of the light source224. At step 420, the switching device S3 is transitioned into the openstate as a result of a 48V signal being applied by the AC-to-DCconverter 216 at the control terminal C_(T) of the switching device S3.At step 430, an indication of a brightness level is received by thecontroller 240. In some implementations, the indication may be a voltagesignal that is generated by the dimmer controller 226 and the dimmerinterface 232 or a message that is received via a communicationsinterface of the controller 240 (e.g., a Bluetooth interface) thatspecifies a selected brightness level. At step 440, the control signalCTRL is output by the controller to the current sources 218 and 222based on the received indication. At step 450, the current sources 218and 222 begin outputting respective PWM signals that are used to drivethe light sources 220 and 224, respectively. As noted above, the PWMsignals may each have a duty cycle that depends on the control signalCTRL.

FIG. 5 is a flowchart of an example of a process 500 that is performedby the system 200 when the system 200 is in the backup power state. Atstep 510, switch S1 is configured to disconnect lines 244 and 246 fromone another, and switch S2 is configured to connect the negativeterminal to the battery 214 to the return path 248 of the light source224. At step 520, the AC-to-DC converter 216 stops outputting a 48V DCsignal as a result of losing its AC voltage supply (e.g., due to amunicipal power grid failure, etc.). At step 530, the controller 240 isswitched off as a result of losing its supply of power from the AC-to-DCconverter 216. When the controller is switched off, the control signalCTRL stops being supplied to the current sources 218 and 222. At step540, the current sources 218 and 222 are disabled due to the loss of thecontrol signal CTRL and they stop supplying respective PWM signals tothe light sources 220 and 224. At step 550, the switching device S3 istransitioned into the closed state (e.g., as a result of the 48V DCoperational voltage no longer being applied at the control terminalC_(T)), which causes current to begin flowing from the battery 214 tothe light source 224.

FIGS. 1-5 are provided as an example only. At least some detail may beomitted from the figures in order to improve clarity. Furthermore, atleast some of the steps in the processes 400 and 500 can be omitted,performed concurrently, or performed in a different order. The presentdisclosure is not limited to any particular order of performing thesteps in the processes 400 and 500, and some or most of these steps canbe performed concurrently. Although the disclosure is provided in thecontext of light-emitting diodes, it will be understood that the system200 is not limited to using light emitting diodes as light sources. Asused throughout the disclosure, the phrase “supply of power isinterrupted” may refer to circumstances in which power is no longersupplied without implying anything about the duration of theinterruption. For example, the interruption may last for any suitabletime period, such as minutes, hours, days, etc. As used throughout thedisclosure, the phrase “supply of AC voltage is interrupted” may referto circumstances in which AC voltage is no longer supplied withoutimplying anything about the duration of the interruption. For example,the interruption may last for any suitable time period, such as minutes,hours, days, etc. At least some of the elements discussed with respectto these figures can be arranged in different order, combined, and/oraltogether omitted. It will be understood that the provision of theexamples described herein, as well as clauses phrased as “such as,”“e.g.”, “including”, “in some aspects,” “in some implementations,” andthe like should not be interpreted as limiting the disclosed subjectmatter to the specific examples.

Having described the invention in detail, those skilled in the art willappreciate that, given the present disclosure, modifications may be madeto the invention without departing from the spirit of the inventiveconcepts described herein. Therefore, it is not intended that the scopeof the invention be limited to the specific embodiments illustrated anddescribed.

What is claimed is:
 1. A system comprising: a light source; a converterconfigured to convert an AC voltage to a DC operating voltage duringnormal operation; a power backup device coupled to the converter; acurrent source having a first terminal configured to receive the DCoperating voltage during regular operation and a second terminalconfigured to provide a pulse-width modulated (PWM) signal to an anodeend of the light source; and a switching device having a firstconnecting terminal coupled to the anode end of the light source, asecond connecting terminal coupled to the power backup device, and acontrol terminal coupled to the converter, the switching deviceconfigured to open a switch between the first connecting terminal andthe second connecting terminal during normal operation and close theswitch upon detecting an interruption of the DC operating voltage at thecontrol terminal.
 2. The system of claim 1, wherein, the switchingdevice is connected to the anode end of the light source and the powerbackup device in parallel.
 3. The system of claim 1, wherein the powerbackup device comprises a battery.
 4. The system of claim 1, wherein thesecond connecting terminal of the switching device is coupled to apositive terminal of the power backup device.
 5. The system of claim 1,wherein the first terminal of the current source is coupled to apositive terminal of the power backup device.
 6. The system of claim 1,further comprising: a first switch within the power backup deviceconfigured to cause the first terminal of the current source to bedisconnected from the converter upon detecting the interruption of theDC operating voltage.
 7. The system of claim 6, further comprising: asecond switch within the power backup device configured to couple acathode end of the light source with a negative terminal of the powerbackup device upon detecting the interruption of the DC operatingvoltage.
 8. The system of claim 1, wherein the current source isarranged on a first electrical path between the light source and thepower backup device, and the switching device is arranged on a secondelectrical path between the light source and the power backup devicethat bypasses the current source.
 9. The system of claim 1, wherein theswitching device includes a PMOS transistor, and the converter isarranged to apply the DC operating voltage on a gate of the PMOStransistor at the control terminal when the supply of AC voltage to theconverter is available.
 10. The system of claim 1, further comprising acontroller, wherein the PWM signal is generated based on a controlsignal received by the current source from the controller.
 11. Thesystem of claim 1, wherein the converter and the power backup device areconnected to an AC power supply.
 12. The system of claim 1, wherein thefirst light source comprises one or more light emitting diodes (LEDs).13. The system of claim 1, further comprising: a second light source;and a second current source having a first terminal configured toreceive the DC operating voltage during regular operation and a secondterminal configured to provide a pulse-width modulated (PWM) signal toan anode end of the second light source.
 14. The system of claim 13,wherein the first source comprises one or more LEDs of a first colortemperature and the second light source comprises one or more LEDs of asecond color temperature.
 15. The system of claim 13, wherein the secondlight source is not powered during the interruption of the DC operatingvoltage.